Feeding of a fat-free diet for an extended period results in essential fatty acid deficiency (EFAD) in many animal species including man especially in infants and weanling animals. Evidence has been obtained that acutely ill neonates and critically ill stressed adults would become EFA deficient within 2-3 days and 2-4 weeks, respectively, when oral feedings are not tolerated. Biochemical deficiency based on the triene (20:3 w9) to tetraene (20:4 w6) ratio of plasma becomes evident within 2-3 weeks in normal young adults fed a fat-free diet. Recently, solutions containing glucose and amino acids or protein hydrolysate along with vitamins and minerals have been given to patients for total parenteral nutrition. As the result of long-term parenteral nutrition devoid of fats, clinical EFAD has been observed. Since there are many nutritionally depleted stressed, ill, hospitalized patients who can take little or no food by mouth, it is likely that the incidence of EFAD is higher than realized. This is true especially in those on total parenteral nutrition without fat. Thus, this project is designed to study: 1) incidence, criteria for early diagnosis of EFAD, 2) prostaglandin synthesis both in EFA deficient and repleted patients in efforts to determine if depletion of EFA will decrease prostaglandin synthesis which may occur in the early phase of EFAD and can be used for early detection of this manifestation, 3) optimal requirement and dosage and route of administration of EFA in correcting deficient changes, 4) the possible changes in red and white blood cell and platelet functions and metabolism as affected by EFAD, 5) morphologic changes of some tissues such as heart, liver, lung, skin, etc. of patients and animals with EFAD. The proposed project emphasize studies in patients. Some aspects of this project will also be studied in puppies and weanling rats.